joinrels.c

/*------------------------------------------------------------------------- * * joinrels.c * Routines to determine which relations should be joined * * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * * * IDENTIFICATION * $PostgreSQL: pgsql/src/backend/optimizer/path/joinrels.c,v 1.100.2.2 2009/07/23 17:42:13 tgl Exp $ * *------------------------------------------------------------------------- */#include "postgres.h"#include "optimizer/joininfo.h"#include "optimizer/pathnode.h"#include "optimizer/paths.h"static List *make_rels_by_clause_joins(PlannerInfo *root,
RelOptInfo *old_rel,
ListCell *other_rels);
static List *make_rels_by_clauseless_joins(PlannerInfo *root,
RelOptInfo *old_rel,
ListCell *other_rels);
staticbool has_join_restriction(PlannerInfo *root, RelOptInfo *rel);
staticbool has_legal_joinclause(PlannerInfo *root, RelOptInfo *rel);
staticbool is_dummy_rel(RelOptInfo *rel);
staticvoid mark_dummy_rel(RelOptInfo *rel);
staticbool restriction_is_constant_false(List *restrictlist);
/* * join_search_one_level * Consider ways to produce join relations containing exactly 'level' * jointree items. (This is one step of the dynamic-programming method * embodied in standard_join_search.) Join rel nodes for each feasible * combination of lower-level rels are created and returned in a list. * Implementation paths are created for each such joinrel, too. * * level: level of rels we want to make this time. * joinrels[j], 1 <= j < level, is a list of rels containing j items. */
List *
join_search_one_level(PlannerInfo *root, int level, List **joinrels)
{
List *result_rels = NIL;
List *new_rels;
ListCell *r;
int k;
/* * First, consider left-sided and right-sided plans, in which rels of * exactly level-1 member relations are joined against initial relations. * We prefer to join using join clauses, but if we find a rel of level-1 * members that has no join clauses, we will generate Cartesian-product * joins against all initial rels not already contained in it. * * In the first pass (level == 2), we try to join each initial rel to each * initial rel that appears later in joinrels[1]. (The mirror-image joins * are handled automatically by make_join_rel.) In later passes, we try * to join rels of size level-1 from joinrels[level-1] to each initial rel * in joinrels[1]. */foreach(r, joinrels[level - 1])
{
RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
ListCell *other_rels;
if (level == 2)
other_rels = lnext(r); /* only consider remaining initial * rels */else
other_rels = list_head(joinrels[1]); /* consider all initial * rels */if (old_rel->joininfo != NIL || old_rel->has_eclass_joins ||
has_join_restriction(root, old_rel))
{
/* * Note that if all available join clauses for this rel require * more than one other rel, we will fail to make any joins against * it here. In most cases that's OK; it'll be considered by * "bushy plan" join code in a higher-level pass where we have * those other rels collected into a join rel. * * See also the last-ditch case below. */
new_rels = make_rels_by_clause_joins(root,
old_rel,
other_rels);
}
else
{
/* * Oops, we have a relation that is not joined to any other * relation, either directly or by join-order restrictions. * Cartesian product time. */
new_rels = make_rels_by_clauseless_joins(root,
old_rel,
other_rels);
}
/* * At levels above 2 we will generate the same joined relation in * multiple ways --- for example (a join b) join c is the same * RelOptInfo as (b join c) join a, though the second case will add a * different set of Paths to it. To avoid making extra work for * subsequent passes, do not enter the same RelOptInfo into our output * list multiple times. */
result_rels = list_concat_unique_ptr(result_rels, new_rels);
}
/* * Now, consider "bushy plans" in which relations of k initial rels are * joined to relations of level-k initial rels, for 2 <= k <= level-2. * * We only consider bushy-plan joins for pairs of rels where there is a * suitable join clause (or join order restriction), in order to avoid * unreasonable growth of planning time. */for (k = 2;; k++)
{
int other_level = level - k;
/* * Since make_join_rel(x, y) handles both x,y and y,x cases, we only * need to go as far as the halfway point. */if (k > other_level)
break;
foreach(r, joinrels[k])
{
RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
ListCell *other_rels;
ListCell *r2;
/* * We can ignore clauseless joins here, *except* when they * participate in join-order restrictions --- then we might have * to force a bushy join plan. */if (old_rel->joininfo == NIL && !old_rel->has_eclass_joins &&
!has_join_restriction(root, old_rel))
continue;
if (k == other_level)
other_rels = lnext(r); /* only consider remaining rels */else
other_rels = list_head(joinrels[other_level]);
for_each_cell(r2, other_rels)
{
RelOptInfo *new_rel = (RelOptInfo *) lfirst(r2);
if (!bms_overlap(old_rel->relids, new_rel->relids))
{
/* * OK, we can build a rel of the right level from this * pair of rels. Do so if there is at least one usable * join clause or a relevant join restriction. */if (have_relevant_joinclause(root, old_rel, new_rel) ||
have_join_order_restriction(root, old_rel, new_rel))
{
RelOptInfo *jrel;
jrel = make_join_rel(root, old_rel, new_rel);
/* Avoid making duplicate entries ... */if (jrel)
result_rels = list_append_unique_ptr(result_rels,
jrel);
}
}
}
}
}
/* * Last-ditch effort: if we failed to find any usable joins so far, force * a set of cartesian-product joins to be generated. This handles the * special case where all the available rels have join clauses but we * cannot use any of those clauses yet. An example is * * SELECT * FROM a,b,c WHERE (a.f1 + b.f2 + c.f3) = 0; * * The join clause will be usable at level 3, but at level 2 we have no * choice but to make cartesian joins. We consider only left-sided and * right-sided cartesian joins in this case (no bushy). */if (result_rels == NIL)
{
/* * This loop is just like the first one, except we always call * make_rels_by_clauseless_joins(). */foreach(r, joinrels[level - 1])
{
RelOptInfo *old_rel = (RelOptInfo *) lfirst(r);
ListCell *other_rels;
if (level == 2)
other_rels = lnext(r); /* only consider remaining initial * rels */else
other_rels = list_head(joinrels[1]); /* consider all initial * rels */
new_rels = make_rels_by_clauseless_joins(root,
old_rel,
other_rels);
result_rels = list_concat_unique_ptr(result_rels, new_rels);
}
/*---------- * When special joins are involved, there may be no legal way * to make an N-way join for some values of N. For example consider * * SELECT ... FROM t1 WHERE * x IN (SELECT ... FROM t2,t3 WHERE ...) AND * y IN (SELECT ... FROM t4,t5 WHERE ...) * * We will flatten this query to a 5-way join problem, but there are * no 4-way joins that join_is_legal() will consider legal. We have * to accept failure at level 4 and go on to discover a workable * bushy plan at level 5. * * However, if there are no special joins then join_is_legal() should * never fail, and so the following sanity check is useful. *---------- */if (result_rels == NIL && root->join_info_list == NIL)
elog(ERROR, "failed to build any %d-way joins", level);
}
return result_rels;
}
/* * make_rels_by_clause_joins * Build joins between the given relation 'old_rel' and other relations * that participate in join clauses that 'old_rel' also participates in * (or participate in join-order restrictions with it). * The join rel nodes are returned in a list. * * 'old_rel' is the relation entry for the relation to be joined * 'other_rels': the first cell in a linked list containing the other * rels to be considered for joining * * Currently, this is only used with initial rels in other_rels, but it * will work for joining to joinrels too. */static List *
make_rels_by_clause_joins(PlannerInfo *root,
RelOptInfo *old_rel,
ListCell *other_rels)
{
List *result = NIL;
ListCell *l;
for_each_cell(l, other_rels)
{
RelOptInfo *other_rel = (RelOptInfo *) lfirst(l);
if (!bms_overlap(old_rel->relids, other_rel->relids) &&
(have_relevant_joinclause(root, old_rel, other_rel) ||
have_join_order_restriction(root, old_rel, other_rel)))
{
RelOptInfo *jrel;
jrel = make_join_rel(root, old_rel, other_rel);
if (jrel)
result = lcons(jrel, result);
}
}
return result;
}
/* * make_rels_by_clauseless_joins * Given a relation 'old_rel' and a list of other relations * 'other_rels', create a join relation between 'old_rel' and each * member of 'other_rels' that isn't already included in 'old_rel'. * The join rel nodes are returned in a list. * * 'old_rel' is the relation entry for the relation to be joined * 'other_rels': the first cell of a linked list containing the * other rels to be considered for joining * * Currently, this is only used with initial rels in other_rels, but it would * work for joining to joinrels too. */static List *
make_rels_by_clauseless_joins(PlannerInfo *root,
RelOptInfo *old_rel,
ListCell *other_rels)
{
List *result = NIL;
ListCell *i;
for_each_cell(i, other_rels)
{
RelOptInfo *other_rel = (RelOptInfo *) lfirst(i);
if (!bms_overlap(other_rel->relids, old_rel->relids))
{
RelOptInfo *jrel;
jrel = make_join_rel(root, old_rel, other_rel);
/* * As long as given other_rels are distinct, don't need to test to * see if jrel is already part of output list. */if (jrel)
result = lcons(jrel, result);
}
}
return result;
}
/* * join_is_legal * Determine whether a proposed join is legal given the query's * join order constraints; and if it is, determine the join type. * * Caller must supply not only the two rels, but the union of their relids. * (We could simplify the API by computing joinrelids locally, but this * would be redundant work in the normal path through make_join_rel.) * * On success, *sjinfo_p is set to NULL if this is to be a plain inner join, * else it's set to point to the associated SpecialJoinInfo node. Also, * *reversed_p is set TRUE if the given relations need to be swapped to * match the SpecialJoinInfo node. */staticbool
join_is_legal(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2,
Relids joinrelids,
SpecialJoinInfo **sjinfo_p, bool *reversed_p)
{
SpecialJoinInfo *match_sjinfo;
bool reversed;
bool unique_ified;
bool is_valid_inner;
ListCell *l;
/* * Ensure output params are set on failure return. This is just to * suppress uninitialized-variable warnings from overly anal compilers. */
*sjinfo_p = NULL;
*reversed_p = false;
/* * If we have any special joins, the proposed join might be illegal; and * in any case we have to determine its join type. Scan the join info * list for conflicts. */
match_sjinfo = NULL;
reversed = false;
unique_ified = false;
is_valid_inner = true;
foreach(l, root->join_info_list)
{
SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
/* * This special join is not relevant unless its RHS overlaps the * proposed join. (Check this first as a fast path for dismissing * most irrelevant SJs quickly.) */if (!bms_overlap(sjinfo->min_righthand, joinrelids))
continue;
/* * Also, not relevant if proposed join is fully contained within RHS * (ie, we're still building up the RHS). */if (bms_is_subset(joinrelids, sjinfo->min_righthand))
continue;
/* * Also, not relevant if SJ is already done within either input. */if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
bms_is_subset(sjinfo->min_righthand, rel1->relids))
continue;
if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
bms_is_subset(sjinfo->min_righthand, rel2->relids))
continue;
/* * If it's a semijoin and we already joined the RHS to any other * rels within either input, then we must have unique-ified the RHS * at that point (see below). Therefore the semijoin is no longer * relevant in this join path. */if (sjinfo->jointype == JOIN_SEMI)
{
if (bms_is_subset(sjinfo->syn_righthand, rel1->relids) &&
!bms_equal(sjinfo->syn_righthand, rel1->relids))
continue;
if (bms_is_subset(sjinfo->syn_righthand, rel2->relids) &&
!bms_equal(sjinfo->syn_righthand, rel2->relids))
continue;
}
/* * If one input contains min_lefthand and the other contains * min_righthand, then we can perform the SJ at this join. * * Barf if we get matches to more than one SJ (is that possible?) */if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
bms_is_subset(sjinfo->min_righthand, rel2->relids))
{
if (match_sjinfo)
returnfalse; /* invalid join path */
match_sjinfo = sjinfo;
reversed = false;
}
elseif (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
bms_is_subset(sjinfo->min_righthand, rel1->relids))
{
if (match_sjinfo)
returnfalse; /* invalid join path */
match_sjinfo = sjinfo;
reversed = true;
}
elseif (sjinfo->jointype == JOIN_SEMI &&
bms_equal(sjinfo->syn_righthand, rel2->relids) &&
create_unique_path(root, rel2, rel2->cheapest_total_path,
sjinfo) != NULL)
{
/*---------- * For a semijoin, we can join the RHS to anything else by * unique-ifying the RHS (if the RHS can be unique-ified). * We will only get here if we have the full RHS but less * than min_lefthand on the LHS. * * The reason to consider such a join path is exemplified by * SELECT ... FROM a,b WHERE (a.x,b.y) IN (SELECT c1,c2 FROM c) * If we insist on doing this as a semijoin we will first have * to form the cartesian product of A*B. But if we unique-ify * C then the semijoin becomes a plain innerjoin and we can join * in any order, eg C to A and then to B. When C is much smaller * than A and B this can be a huge win. So we allow C to be * joined to just A or just B here, and then make_join_rel has * to handle the case properly. * * Note that actually we'll allow unique-ified C to be joined to * some other relation D here, too. That is legal, if usually not * very sane, and this routine is only concerned with legality not * with whether the join is good strategy. *---------- */if (match_sjinfo)
returnfalse; /* invalid join path */
match_sjinfo = sjinfo;
reversed = false;
unique_ified = true;
}
elseif (sjinfo->jointype == JOIN_SEMI &&
bms_equal(sjinfo->syn_righthand, rel1->relids) &&
create_unique_path(root, rel1, rel1->cheapest_total_path,
sjinfo) != NULL)
{
/* Reversed semijoin case */if (match_sjinfo)
returnfalse; /* invalid join path */
match_sjinfo = sjinfo;
reversed = true;
unique_ified = true;
}
else
{
/*---------- * Otherwise, the proposed join overlaps the RHS but isn't * a valid implementation of this SJ. It might still be * a legal join, however. If both inputs overlap the RHS, * assume that it's OK. Since the inputs presumably got past * this function's checks previously, they can't overlap the * LHS and their violations of the RHS boundary must represent * SJs that have been determined to commute with this one. * We have to allow this to work correctly in cases like * (a LEFT JOIN (b JOIN (c LEFT JOIN d))) * when the c/d join has been determined to commute with the join * to a, and hence d is not part of min_righthand for the upper * join. It should be legal to join b to c/d but this will appear * as a violation of the upper join's RHS. * Furthermore, if one input overlaps the RHS and the other does * not, we should still allow the join if it is a valid * implementation of some other SJ. We have to allow this to * support the associative identity * (a LJ b on Pab) LJ c ON Pbc = a LJ (b LJ c ON Pbc) on Pab * since joining B directly to C violates the lower SJ's RHS. * We assume that make_outerjoininfo() set things up correctly * so that we'll only match to some SJ if the join is valid. * Set flag here to check at bottom of loop. *---------- */if (sjinfo->jointype != JOIN_SEMI &&
bms_overlap(rel1->relids, sjinfo->min_righthand) &&
bms_overlap(rel2->relids, sjinfo->min_righthand))
{
/* seems OK */
Assert(!bms_overlap(joinrelids, sjinfo->min_lefthand));
}
else
is_valid_inner = false;
}
}
/* * Fail if violated some SJ's RHS and didn't match to another SJ. * However, "matching" to a semijoin we are implementing by * unique-ification doesn't count (think: it's really an inner join). */if (!is_valid_inner &&
(match_sjinfo == NULL || unique_ified))
returnfalse; /* invalid join path *//* Otherwise, it's a valid join */
*sjinfo_p = match_sjinfo;
*reversed_p = reversed;
returntrue;
}
/* * make_join_rel * Find or create a join RelOptInfo that represents the join of * the two given rels, and add to it path information for paths * created with the two rels as outer and inner rel. * (The join rel may already contain paths generated from other * pairs of rels that add up to the same set of base rels.) * * NB: will return NULL if attempted join is not valid. This can happen * when working with outer joins, or with IN or EXISTS clauses that have been * turned into joins. */
RelOptInfo *
make_join_rel(PlannerInfo *root, RelOptInfo *rel1, RelOptInfo *rel2)
{
Relids joinrelids;
SpecialJoinInfo *sjinfo;
bool reversed;
SpecialJoinInfo sjinfo_data;
RelOptInfo *joinrel;
List *restrictlist;
/* We should never try to join two overlapping sets of rels. */
Assert(!bms_overlap(rel1->relids, rel2->relids));
/* Construct Relids set that identifies the joinrel. */
joinrelids = bms_union(rel1->relids, rel2->relids);
/* Check validity and determine join type. */if (!join_is_legal(root, rel1, rel2, joinrelids,
&sjinfo, &reversed))
{
/* invalid join path */
bms_free(joinrelids);
return NULL;
}
/* Swap rels if needed to match the join info. */if (reversed)
{
RelOptInfo *trel = rel1;
rel1 = rel2;
rel2 = trel;
}
/* * If it's a plain inner join, then we won't have found anything in * join_info_list. Make up a SpecialJoinInfo so that selectivity * estimation functions will know what's being joined. */if (sjinfo == NULL)
{
sjinfo = &sjinfo_data;
sjinfo->type = T_SpecialJoinInfo;
sjinfo->min_lefthand = rel1->relids;
sjinfo->min_righthand = rel2->relids;
sjinfo->syn_lefthand = rel1->relids;
sjinfo->syn_righthand = rel2->relids;
sjinfo->jointype = JOIN_INNER;
/* we don't bother trying to make the remaining fields valid */
sjinfo->lhs_strict = false;
sjinfo->delay_upper_joins = false;
sjinfo->join_quals = NIL;
}
/* * Find or build the join RelOptInfo, and compute the restrictlist that * goes with this particular joining. */
joinrel = build_join_rel(root, joinrelids, rel1, rel2, sjinfo,
&restrictlist);
/* * If we've already proven this join is empty, we needn't consider any * more paths for it. */if (is_dummy_rel(joinrel))
{
bms_free(joinrelids);
return joinrel;
}
/* * Consider paths using each rel as both outer and inner. Depending on * the join type, a provably empty outer or inner rel might mean the join * is provably empty too; in which case throw away any previously computed * paths and mark the join as dummy. (We do it this way since it's * conceivable that dummy-ness of a multi-element join might only be * noticeable for certain construction paths.) * * Also, a provably constant-false join restriction typically means that * we can skip evaluating one or both sides of the join. We do this by * marking the appropriate rel as dummy. * * We need only consider the jointypes that appear in join_info_list, plus * JOIN_INNER. */switch (sjinfo->jointype)
{
case JOIN_INNER:
if (is_dummy_rel(rel1) || is_dummy_rel(rel2) ||
restriction_is_constant_false(restrictlist))
{
mark_dummy_rel(joinrel);
break;
}
add_paths_to_joinrel(root, joinrel, rel1, rel2,
JOIN_INNER, sjinfo,
restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1,
JOIN_INNER, sjinfo,
restrictlist);
break;
case JOIN_LEFT:
if (is_dummy_rel(rel1))
{
mark_dummy_rel(joinrel);
break;
}
if (restriction_is_constant_false(restrictlist) &&
bms_is_subset(rel2->relids, sjinfo->syn_righthand))
mark_dummy_rel(rel2);
add_paths_to_joinrel(root, joinrel, rel1, rel2,
JOIN_LEFT, sjinfo,
restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1,
JOIN_RIGHT, sjinfo,
restrictlist);
break;
case JOIN_FULL:
if (is_dummy_rel(rel1) && is_dummy_rel(rel2))
{
mark_dummy_rel(joinrel);
break;
}
add_paths_to_joinrel(root, joinrel, rel1, rel2,
JOIN_FULL, sjinfo,
restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1,
JOIN_FULL, sjinfo,
restrictlist);
break;
case JOIN_SEMI:
/* * We might have a normal semijoin, or a case where we don't have * enough rels to do the semijoin but can unique-ify the RHS and * then do an innerjoin (see comments in join_is_legal). In the * latter case we can't apply JOIN_SEMI joining. */if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
bms_is_subset(sjinfo->min_righthand, rel2->relids))
{
if (is_dummy_rel(rel1) || is_dummy_rel(rel2) ||
restriction_is_constant_false(restrictlist))
{
mark_dummy_rel(joinrel);
break;
}
add_paths_to_joinrel(root, joinrel, rel1, rel2,
JOIN_SEMI, sjinfo,
restrictlist);
}
/* * If we know how to unique-ify the RHS and one input rel is * exactly the RHS (not a superset) we can consider unique-ifying * it and then doing a regular join. (The create_unique_path * check here is probably redundant with what join_is_legal did, * but if so the check is cheap because it's cached. So test * anyway to be sure.) */if (bms_equal(sjinfo->syn_righthand, rel2->relids) &&
create_unique_path(root, rel2, rel2->cheapest_total_path,
sjinfo) != NULL)
{
add_paths_to_joinrel(root, joinrel, rel1, rel2,
JOIN_UNIQUE_INNER, sjinfo,
restrictlist);
add_paths_to_joinrel(root, joinrel, rel2, rel1,
JOIN_UNIQUE_OUTER, sjinfo,
restrictlist);
}
break;
case JOIN_ANTI:
if (is_dummy_rel(rel1))
{
mark_dummy_rel(joinrel);
break;
}
if (restriction_is_constant_false(restrictlist) &&
bms_is_subset(rel2->relids, sjinfo->syn_righthand))
mark_dummy_rel(rel2);
add_paths_to_joinrel(root, joinrel, rel1, rel2,
JOIN_ANTI, sjinfo,
restrictlist);
break;
default:
/* other values not expected here */
elog(ERROR, "unrecognized join type: %d", (int) sjinfo->jointype);
break;
}
bms_free(joinrelids);
return joinrel;
}
/* * have_join_order_restriction * Detect whether the two relations should be joined to satisfy * a join-order restriction arising from special joins. * * In practice this is always used with have_relevant_joinclause(), and so * could be merged with that function, but it seems clearer to separate the * two concerns. We need this test because there are degenerate cases where * a clauseless join must be performed to satisfy join-order restrictions. * * Note: this is only a problem if one side of a degenerate outer join * contains multiple rels, or a clauseless join is required within an * IN/EXISTS RHS; else we will find a join path via the "last ditch" case in * join_search_one_level(). We could dispense with this test if we were * willing to try bushy plans in the "last ditch" case, but that seems much * less efficient. */bool
have_join_order_restriction(PlannerInfo *root,
RelOptInfo *rel1, RelOptInfo *rel2)
{
bool result = false;
ListCell *l;
/* * It's possible that the rels correspond to the left and right sides of a * degenerate outer join, that is, one with no joinclause mentioning the * non-nullable side; in which case we should force the join to occur. * * Also, the two rels could represent a clauseless join that has to be * completed to build up the LHS or RHS of an outer join. */foreach(l, root->join_info_list)
{
SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
/* ignore full joins --- other mechanisms handle them */if (sjinfo->jointype == JOIN_FULL)
continue;
/* Can we perform the SJ with these rels? */if (bms_is_subset(sjinfo->min_lefthand, rel1->relids) &&
bms_is_subset(sjinfo->min_righthand, rel2->relids))
{
result = true;
break;
}
if (bms_is_subset(sjinfo->min_lefthand, rel2->relids) &&
bms_is_subset(sjinfo->min_righthand, rel1->relids))
{
result = true;
break;
}
/* * Might we need to join these rels to complete the RHS? We have to * use "overlap" tests since either rel might include a lower SJ that * has been proven to commute with this one. */if (bms_overlap(sjinfo->min_righthand, rel1->relids) &&
bms_overlap(sjinfo->min_righthand, rel2->relids))
{
result = true;
break;
}
/* Likewise for the LHS. */if (bms_overlap(sjinfo->min_lefthand, rel1->relids) &&
bms_overlap(sjinfo->min_lefthand, rel2->relids))
{
result = true;
break;
}
}
/* * We do not force the join to occur if either input rel can legally be * joined to anything else using joinclauses. This essentially means that * clauseless bushy joins are put off as long as possible. The reason is * that when there is a join order restriction high up in the join tree * (that is, with many rels inside the LHS or RHS), we would otherwise * expend lots of effort considering very stupid join combinations within * its LHS or RHS. */if (result)
{
if (has_legal_joinclause(root, rel1) ||
has_legal_joinclause(root, rel2))
result = false;
}
return result;
}
/* * has_join_restriction * Detect whether the specified relation has join-order restrictions * due to being inside an outer join or an IN (sub-SELECT). * * Essentially, this tests whether have_join_order_restriction() could * succeed with this rel and some other one. It's OK if we sometimes * say "true" incorrectly. (Therefore, we don't bother with the relatively * expensive has_legal_joinclause test.) */staticbool
has_join_restriction(PlannerInfo *root, RelOptInfo *rel)
{
ListCell *l;
foreach(l, root->join_info_list)
{
SpecialJoinInfo *sjinfo = (SpecialJoinInfo *) lfirst(l);
/* ignore full joins --- other mechanisms preserve their ordering */if (sjinfo->jointype == JOIN_FULL)
continue;
/* ignore if SJ is already contained in rel */if (bms_is_subset(sjinfo->min_lefthand, rel->relids) &&
bms_is_subset(sjinfo->min_righthand, rel->relids))
continue;
/* restricted if it overlaps LHS or RHS, but doesn't contain SJ */if (bms_overlap(sjinfo->min_lefthand, rel->relids) ||
bms_overlap(sjinfo->min_righthand, rel->relids))
returntrue;
}
returnfalse;
}
/* * has_legal_joinclause * Detect whether the specified relation can legally be joined * to any other rels using join clauses. * * We consider only joins to single other relations in the current * initial_rels list. This is sufficient to get a "true" result in most real * queries, and an occasional erroneous "false" will only cost a bit more * planning time. The reason for this limitation is that considering joins to * other joins would require proving that the other join rel can legally be * formed, which seems like too much trouble for something that's only a * heuristic to save planning time. (Note: we must look at initial_rels * and not all of the query, since when we are planning a sub-joinlist we * may be forced to make clauseless joins within initial_rels even though * there are join clauses linking to other parts of the query.) */staticbool
has_legal_joinclause(PlannerInfo *root, RelOptInfo *rel)
{
ListCell *lc;
foreach(lc, root->initial_rels)
{
RelOptInfo *rel2 = (RelOptInfo *) lfirst(lc);
/* ignore rels that are already in "rel" */if (bms_overlap(rel->relids, rel2->relids))
continue;
if (have_relevant_joinclause(root, rel, rel2))
{
Relids joinrelids;
SpecialJoinInfo *sjinfo;
bool reversed;
/* join_is_legal needs relids of the union */
joinrelids = bms_union(rel->relids, rel2->relids);
if (join_is_legal(root, rel, rel2, joinrelids,
&sjinfo, &reversed))
{
/* Yes, this will work */
bms_free(joinrelids);
returntrue;
}
bms_free(joinrelids);
}
}
returnfalse;
}
/* * is_dummy_rel --- has relation been proven empty? * * If so, it will have a single path that is dummy. */staticbool
is_dummy_rel(RelOptInfo *rel)
{
return (rel->cheapest_total_path != NULL &&
IS_DUMMY_PATH(rel->cheapest_total_path));
}
/* * Mark a rel as proven empty. */staticvoid
mark_dummy_rel(RelOptInfo *rel)
{
/* Set dummy size estimate */
rel->rows = 0;
/* Evict any previously chosen paths */
rel->pathlist = NIL;
/* Set up the dummy path */
add_path(rel, (Path *) create_append_path(rel, NIL));
/* Set or update cheapest_total_path */
set_cheapest(rel);
}
/* * restriction_is_constant_false --- is a restrictlist just FALSE? * * In cases where a qual is provably constant FALSE, eval_const_expressions * will generally have thrown away anything that's ANDed with it. In outer * join situations this will leave us computing cartesian products only to * decide there's no match for an outer row, which is pretty stupid. So, * we need to detect the case. */staticbool
restriction_is_constant_false(List *restrictlist)
{
ListCell *lc;
/* * Despite the above comment, the restriction list we see here might * possibly have other members besides the FALSE constant, since other * quals could get "pushed down" to the outer join level. So we check * each member of the list. */foreach(lc, restrictlist)
{
RestrictInfo *rinfo = (RestrictInfo *) lfirst(lc);
Assert(IsA(rinfo, RestrictInfo));
if (rinfo->clause && IsA(rinfo->clause, Const))
{
Const *con = (Const *) rinfo->clause;
/* constant NULL is as good as constant FALSE for our purposes */
if (con->constisnull)
returntrue;
if (!DatumGetBool(con->constvalue))
returntrue;
}
}
returnfalse;
}